Experimental analysis on friction materials for supplemental damping devices

In this paper, the friction coefficient and the cyclic response of different interfaces for friction devices are investigated by means of experimental tests under displacement control. In particular, six interfaces have been tested: steel–steel, brass–steel, sprayed aluminum–steel and three different rubber based friction materials adopted, respectively, in automotive applications, electrical machines and applications requiring low wearing.Static and kinetic friction coefficients have been evaluated and the influence of the interface pressure has been analyzed. The variation of the sliding force during the cyclic loading history has been investigated by comparing also the response coming from the use of different washers: circular flat washers and cone shaped annular disc springs.The work is aimed at the investigation of friction materials to be applied within the connecting elements of beam-to-column joints according to the double split tee configuration with friction pads.

Discovery of a nearby 1700 km s−1 star ejected from the Milky Way by Sgr A*

ABSTRACT We present the serendipitous discovery of the fastest main-sequence hyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey (S5). The star S5-HVS1 is a ∼2.35 M⊙ A-type star located at a distance of ∼9 kpc from the Sun and has a heliocentric radial velocity of 1017 ± 2.7 $\mathrm{\, km\, s^{-1}}$ without any signature of velocity variability. The current 3D velocity of the star in the Galactic frame is 1755 ± 50 $\mathrm{\, km\, s^{-1}}$. When integrated backwards in time, the orbit of the star points unambiguously to the Galactic Centre, implying that S5-HVS1 was kicked away from Sgr A* with a velocity of ∼1800 $\mathrm{\, km\, s^{-1}}$ and travelled for 4.8 Myr to its current location. This is so far the only HVS confidently associated with the Galactic Centre. S5-HVS1 is also the first hyper-velocity star to provide constraints on the geometry and kinematics of the Galaxy, such as the Solar motion Vy,⊙ = 246.1 ± 5.3 $\mathrm{\, km\, s^{-1}}$ or position R0 = 8.12 ± 0.23 kpc. The ejection trajectory and transit time of S5-HVS1 coincide with the orbital plane and age of the annular disc of young stars at the Galactic Centre, and thus may be linked to its formation. With the S5-HVS1 ejection velocity being almost twice the velocity of other hyper-velocity stars previously associated with the Galactic Centre, we question whether they have been generated by the same mechanism or whether the ejection velocity distribution has been constant over time.

Development of finite difference formulation for non-linear analysis of thermal stresses in a thick annular disc

This paper is an attempt to study the impact of temperature dependent thermal properties on thermal stress analysis in a thick annular disc. The upper surface of the disc is subjected to heat transfer due to radiation. The rate of radiation is calculated by Stefan Boltzmann law. Heat dissipates by convection from the lower boundary surface to the surrounding medium. The fixed circular boundaries are kept insulated. Due to temperature dependent thermal properties the governing boundary value problem is perfectly nonlinear, thus one has to adopt the numerical techniques to obtain the mathematical solution. The finite difference formulation for multidimensional cylindrical systems has been developed to compute the temperature change, displacement and thermal stresses in a thick annular disc. Also stability and convergence of obtained numerical results has been done by the fundamental theory of numerical analysis.